1. Field
Embodiments of the present invention relate generally to high-capacity energy storage devices, and more specifically, to batteries having integrated separators and methods of fabricating such batteries.
2. Description of the Related Art
Fast-charging, high-capacity energy storage devices, such as supercapacitors and lithium-ion (Li-ion) batteries, are used in a growing number of applications, including portable electronics, medical, transportation, grid-connected large energy storage, renewable energy storage, and uninterruptible power supply (UPS).
Li-ion batteries typically include an anode electrode, a cathode electrode and a separator positioned between the anode electrode and the cathode electrode. The separator is an electronic insulator which provides physical and electrical separation between the cathode and the anode electrodes. The separator is typically made from micro-porous polyethylene and polyolefin, and is applied in a separate manufacturing step. During electrochemical reactions, i.e., charging and discharging, Li-ions are transported through the pores in the separator between the two electrodes via an electrolyte. Thus, high porosity is desirable to increase ionic conductivity. However, some high porosity separators are susceptible to electrical shorts when lithium dendrites formed during cycling create shorts between the electrodes.
Currently, battery cell manufacturers purchase separators, which are then laminated together with anode and cathode electrodes in separate processing steps. Other separators are made by wet or dry extrusion of a polymer and then stretched to produce holes (tears) in the polymer. The separator is also one of the most expensive components in the Li-ion battery and accounts for over 20% of the material cost in battery cells.
For most energy storage applications, the charge time and capacity of energy storage devices are important parameters. In addition, the size, weight, and/or expense of such energy storage devices can be significant limitations. The use of current separators has a number of drawbacks. Namely, such materials limit the minimum size of the electrodes constructed from such materials, suffer from electrical shorts, require complex manufacturing methods, and expensive materials.
Accordingly, there is a need in the art for faster charging, higher capacity energy storage devices with separators that are smaller, lighter, and can be more cost effectively manufactured.